This invention relates to improved silica packings for use in chromatographic analysis and to a process for making them. It relates particularly to finely divided silica supports having a very thin polymeric organic film chemically bonded to their surface.
The problem of optimizing chromatographic performance is one that has persisted throughout the history of chromatographic separations. Although significant advances have been made in the application of gas-liquid chromatography to analytical problems, most of these have resulted from improvements in apparatus rather than in the column packing itself.
In order to avoid or minimize problems caused by active sites on the surface of a silica chromatographic column packing, coated packings have been prepared by heating an activated silica with an appropriate alcohol under conditions which allow continuous removal of water, thereby causing etherification of the alcohol with silanol groups on the silica surface, see Halasz et al., J. Chrom. Sci., 12, 161 (1974). However, the coating obtained is often not uniform and the method gives poor reproducibility. Stehl, U.S. Pat. No. 3,664,967 describes a method whereby a silica or alumina gel is reacted with an organohalosilane, the halosilane groups thus attached to the surface are reacted with an alcohol and the product is halogenated to provide a haloorganic coating bonded to the support surface. However, the improved chromatographic packings thus obtained are still not entirely satisfactory.